Landis, who tested positive for the banned male hormone testosterone during the 2006 Tour de France, can appeal the verdict of the arbitration panel to the Court of Arbitration for Sport, a move that had been expected by Landis or the US Anti-Doping Agency (USADA), whichever lost the decision from the appeal.
"He has been found guilty," Pat McQuaid, UCI president, told Reuters by telephone.
"It proves that the system works no matter who you are."
The verdict comes almost four months after the longest anti-doping hearing in US history, a rare public session in May in which Landis' lawyers questioned the chain of command from the French laboratory that handles Landis' testing.
Landis said in a statement: "This ruling is a blow to athletes and cyclists everywhere.
"This ruling is a blow to athletes and cyclists everywhere... I am innocent, and we proved I am innocent."
Floyd Landis, US cyclist
"For the Panel to find in favour of USADA (United States Anti-Doping Agency) when, with respect to so many issues, USADA did not manage to prove even the most basic parts of their case shows that this system is fundamentally flawed.
"I am innocent, and we proved I am innocent," the 31-year-old added.
The fall from grace
Landis, who was leading the Tour de France, lost the yellow jersey after a disastrous stage 16 in the Alps on July 19 last year, falling more than eight minutes behind leader Oscar Pereiro of Spain.
The following day, Landis made a miraculous return to form by winning the 17th stage after a daring raid of 130km, putting him just 30 seconds behind race leader Pereiro, with the American going on to win the Tour on July 23.
Four days later, the International Cycling Union (UCI) announced that an unidentified Tour de France rider had tested positive for a performance-enhancing substance, with Landis prompting speculation by withdrawing from races in Denmark and the Netherlands.
The Phonak team confirmed Landis's 'A' sample tested positive for an abnormal level of testosterone, but he denied doping in a teleconference with US reporters.
On August 5, the UCI announced Landis's 'B' sample confirmed the 'A' result, after which Phonak sacked him and Tour de France officials declared they no longer considered him the race champion, although he couldn't be stripped of the title until an adjudication process had been completed.
In April this year, arbitrators voted 2-1 to allow testing of Landis 'B' samples at the French lab that conducted original Tour de France tests, as French sports daily L'Equipe quoted an anonymous source as saying several of the samples showed the presence of synthetic testosterone.
The following month a nine-day arbitration hearing was conducted where Landis and USADA present their case to a three-person arbitration panel.
Arbitrators Patrice Brunet and Richard McLaren ruled against Landis, while Christopher Campbell dissented.
The Landis camp, who challenged the accuracy and reliability of test procedures of the French AFLD lab and the competency of its findings, said their loss showed athletes cannot win through the appeal system.
"This is a miscarriage of justice." said Maurice Suh, Landis's lawyer .
"The majority panel's decision is a disappointment, but particularly so because it failed to address the joint impact of the many errors that the AFLD laboratory committed in rendering this false positive.
"To take each of these errors singly is to ignore the total falsity of the result. The majority panel has disregarded the testimony of Mr. Landis' experts, who are pre-eminent in their respective fields, without analysing the impact of the errors on the final result."
Should all of Landis' avenues of appeal fail, he would have forfeit his 2006 Tour de France title with Pereiro declared the winner.